If you are thinking of buying a telescope for the first time, chances are you will have been doing a little bit of research online. Whilst carrying out your research you will have most likely discovered aspects which you aren’t familiar with and encountered terms which you don’t fully understand. This is quite normal. Indeed, part of the beauty of astronomy is that it often throws up as many questions as it does answers. If you have an enquiring mind then you will enjoy this aspect almost as much as scanning the Heavens.

However, when you’re first starting out, there are a few things which you really do need to have a good understanding of. And, when it comes to buying astronomical telescopes, nothing is more important than aperture.

Basically, a telescope’s aperture is the diameter of its main, light-gathering lens or mirror. (This lens or mirror is called the telescope’s ‘objective’.) The bigger the aperture is, the sharper and brighter your view through the telescope will be. As you have probably realised, a bigger aperture allows you to use more magnification. In fact, you can make any telescope provide any magnification you like, just by changing eyepieces. However, high magnification is worthless without large aperture (indeed, you’ll end up with a dim, blurry, mess).

A telescope which can only be pushed to 50 times magnification (50x) before the view goes blurry will enable you to see Jupiter’s moons, Saturn’s rings, and some detail in the brightest star clusters, nebulae, and galaxies. However, if you’re looking to explore surface features on Mars or see both members of a tight double star, you will need to have the sharp views which a telescope at 150x can deliver. Depending on optical quality (and observing conditions), you can expect to get anywhere from 20x to 50x of useful magnification per inch of aperture. Put another way, a four-inch telescope will manage 200x whereas a six-inch telescope will go as high as 300x, if they are both used under ideal conditions.

Another important feature of large aperture is that it lets you view fainter objects. This is different from providing magnification. In fact, the problem with most hard-to-see astronomical objects is not that they’re too small and need more magnification; it’s that that they’re too faint and need more light i.e. more aperture. For example, there are several dozen galaxies beyond our own Milky Way which can be distinguished through a 4½-inch reflector. Some of these galaxies are more than 50 million light-years away, so being able to see them with a telescope which can be comfortably tucked under your arm really is pretty good. Of course, it is worth noting that a 12½-inch Dobsonian telescope will reveal literally hundreds of far away galaxies, even when you use the same magnification!

If you’d like to find out even more about aperture and browse through a great range of beginners telescopes in detail, simply take a few moments to explore our pages further.